Typically, buffered optical fibers are used for outdoor telecommunications networks. To allow the optical-fiber cable to feed different buildings, the buffered optical fibers of the cable need to be accessible. To access the optical fibers, an operator makes an opening in the cable to extract one or more buffered optical fibers, which are then directed toward the building that is to be served.
Typically, optical fibers have a standard diameter of about 250 microns (μm). The diameter of the optical fiber typically includes an optical-fiber core, a cladding surrounding the core, and a coating surrounding the cladding. The core of the optical fiber transmits an optical signal. The cladding confines the optical signal in the fiber core, and the coating protects the cladding.
When a protective sheath (e.g., a buffer or buffer material) is employed to surround the optical fiber, the resulting diameter of the optical fiber and protective sheath is about 900 microns. This protective sheath provides sealing and protection against impacts and facilitates handling of the fiber.
Buffered optical fibers are typically positioned loosely within a cable, so that it is easy for an operator to extract one or more optical fibers from the cable. Buffered optical fibers used in outdoor telecommunications networks are generally either tightly buffered within a protective sheath (i.e., a tight-buffered fiber) or semi-tightly buffered (i.e., a semi-tight buffered fiber) within a protective sheath.
Tight-buffered fibers are robust and typically remain stable over the usual utilization temperature range (e.g., about −40° C. to +70° C.). Tight-buffered fibers, however, present some drawbacks. In particular, after extracting a tight-buffered optical fiber from the cable, the operator typically also removes the optical fiber (i.e., the fiber core, the cladding, and the coating) from the protective sheath.
Typically, only a few centimeters of the optical fiber can be removed from the protective sheath, because the bonding between the optical fiber and the protective sheath is strong. In this regard, separating more than a few centimeters of the optical fiber from its protective sheath typically tears the coating of the optical fiber away from the cladding.
To alleviate the drawbacks of tight-buffered fibers, semi-tight buffered fibers have been proposed. In a typical semi-tight structure, the optical fiber and the protective sheath of the fiber are not in direct contact but are decoupled. In this regard, there is a gap between the optical fiber and its protective sheath.
As a result, for semi-tight buffered fibers, much greater lengths of optical fiber can be removed from the protective sheath than with a cable having tight-buffered optical fibers. Typically, a few meters of optical fiber can be removed from the protective sheath.
Nevertheless, decoupling the optical fiber and its protective sheath has drawbacks. When an operator extracts a semi-tight buffered fiber from the cable, the extraction force is applied to the protective sheath, which can then slide relative to the optical fiber. Such sliding can give rise to an offset between the length of the optical fiber and the length of the protective sheath. This offset can lead to attenuation in the signal transported by the optical fiber core.
The previously discussed problems are not limited to buffered optical fibers employed in outdoor telecommunications networks and can be encountered whenever a buffered optical fiber is extracted from a cable.
One solution to the attenuation problem that can be caused by the gap between the optical fiber and the protective sheath (e.g., attenuation caused by the sliding of the optical fiber within the protective sheath) includes placing an intermediate layer between the optical fiber and the protective sheath.
For example, U.S. Pat. No. 5,181,268, which is hereby incorporated by reference, proposes an intermediate layer of a lubricant (e.g., polytetrafluoroethylene, such as TEFLON®) and a solid binder (e.g., an acrylic polymer).
European Patent No. 0690033, (and its counterpart U.S. Pat. No. 5,408,564) which is hereby incorporated by reference, proposes a cross-linked intermediate layer including an ultra-high molecular weight polyethylene (UHMWPE) or TEFLON® mixed with a photo-curable binder such as a urethane polymer.
U.S. Pat. No. 6,775,443, which is hereby incorporated by reference, proposes a cross-linked intermediate layer including a matrix of urethane acrylate including oligomers, monomers, a photoinitiator, and an antioxidant combined with a liquid release reagent (e.g., liquid silicone).
Nevertheless, using polytetrafluoroethylene (e.g., TEFLON®) in the buffered optical fibers is not compatible with existing standards. TEFLON® includes fluorine and, as such, is not suitable for cabling a building. Furthermore, the use of curable materials requires additional manufacturing steps (e.g., passing the buffered optical fiber under an ultraviolet (UV) lamp).
Buffered optical fibers may include a mechanical reinforcement to increase the longitudinal strength of the buffered optical fiber. For example, U.K. Patent Application Publication No. GB 2,096,343, which is hereby incorporated by reference, discloses a buffered optical fiber of semi-tight structure (i.e., a semi-tight buffered fiber) that includes aramid strands placed along the axis of the buffered optical fiber in the gap between the optical fiber and the protective sheath. The aramid strands, however, do not couple the optical fiber and its protective sheath.
In view of the foregoing, there is a need for a buffered optical fiber structure that protects the optical fiber contained therein and facilitates the removal of optical fibers from the buffered optical fiber structure.